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Steep agricultural hillslopes are not only subjected to soil erosion, but also have a probability
of failure. In hilly country were both soil erosion and landslide processes are active, the interaction
between these processes is critical. A model called WEPP-SLIP was developed that integrates erosion
modeling and landslide prediction to determine sediment delivery pre and post landslide failures. Initially,
WEPP is used to estimate pre-failure erosion. The landslide model then predicts where a mass failure may
occur along the slope. Changes in topography and soil structure are estimated from the predicted
magnitude of the landslide. The WEPP model is then used again with the new topography to predict postfailure
erosion. A flume based experiment was used to validate the modeling with loess and sandy type soil
representative of hilly sheep pasture land in New Zealand. Results showed a good correlation between
predicted and measured erosion and runoff. In fallow conditions, post-failure erosion was shown to be
smaller than pre-failure erosion due to changes in slope and soil properties resulting from the failure. The
opposite is true for hillslopes covered with grass, as slope failures disturb the cover resulting in greater
erosion. Flume based results indicate that sediment yields during failures were high. WEPP-SLIP can be
applied for individual hillslope profiles; however, efforts are on the way to create a spatially distributed
model. The model will be used to improve management practices and calculate the long term implications of
mass movements in hilly slopes.

Subjects

landslides

erosion

WEPP

steep slopes

modeling

Fields of Research::300000 Agricultural, Veterinary and Environmental Sciences::300100 Soil and Water Sciences